Neogene deformation and granite emplacement in the metamorphic units of northern Apennines (Italy): Insights from mylonitic marbles in the Porto Azzurro pluton contact aureole (Elba Island)

In the northern Tyrrhenian Sea, late Miocene \udintrusions (Monte Capanne pluton and\udPorto Azzurro pluton) were emplaced at\udupper crustal levels (<0.2 GPa) in the thrust\udsystems of Elba Island. The emplacement\udof intrusive rocks is currently explained\udin the context of late Miocene extensional\udtec tonics. New detailed structural data\udcollected along a continuous natural cross\udsection through the contact aureole of the\udPorto Azzurro pluton (eastern Elba) where\udstrain localization has occurred within two\udwest-dipping decameter-scale carbonate\udshear zones, namely the Calanchiole and\udFelciaio shear zones, are reported here.\udThese shear zones, characterized by a lithological\uddifference with calcite and dolomite\udmarbles dominant in the Calanchiole and\udFelciaio shear zones, respectively, exhibit\uda similar rheological behavior . They represent\udtwo weakened layers in which westdipping\udmylonitic foliation, sheath folds,\udboudinage structures, and upright folds\uddeveloped within the contact aureole .\udMoreover, in correspondence with the\udFelciaio shear zone, the inversion of metamorphic\udfacies occurs. Meso- and microstructural\uddata give evidence that most of\udthe deformation and displacement in the\udshear zones was coeval with contact metamorphism\udand developed under metamorphic\udconditions retrograde from pyroxene\udhornfels to hornblende-hornfels facies.\udGeometric and kinematic features indicate\udthat both shear zones correspond to ductile\udthrusts, which led to internal stacking of the\udcontact aureole . Therefore, at Elba Island,\udemplacement of intrusive rocks coeval with\udlate Miocene crustal shortening gives a new\udperspective on relations between tectonics\udand magmatism in the northern Apennines